| 摘要 |
Selective bromination of alkylarenes to the alpha dibrominated derivative is desirable as a precursor for the selective production of, for example, the corresponding aromatic aldehyde. Improvements in the extent of selectivity of the product and/or its rate of production can be obtained by employing a photolytic reaction between the substrate, hydrogen peroxide and hydrogen bromide using mole ratios of H2O2:substrate of about 2.8:1 or higher, preferably 3.2: to 3.5:1 and of bromide:substrate of over 2.5:1, preferably about 2.8:1 to 3.2:1 and progressive controlled introduction of the H2O2, the reaction being carried out in the presence of a substantial amount of an organic solvent, and preferably more than 5.5 volumes per volume of substrate, whilst irradiating with light preferably having principal emissions in the range of 250 to 600 nm. The reaction mixture is preferably maintained at 50 to 60 DEG C. The reaction often takes from 5 to 12 hours, of which period hydrogen peroxide is introduced progressively into the reaction mixture during preferably the first 3 to 5 hours. The process is especially suitable for deactivated alkylarenes, such as o-nitrotoluene. |
